Simultaneous switching noise (SSN) is one form of noise that can exist in electronic systems. SSN can be caused by a substantial number of drivers switching in the same direction within a short time window. Effects of a substantial number of such switching can include dips or spikes in the voltage supply to the chip and can propagate as noise through both active and inactive drivers.
In extreme cases, SSN can prevent proper functioning of the electronic system. For example, disruption to voltage levels of power and/or ground planes in a chip can prevent logic circuitry from functioning correctly. If a logic 1 output from a gate array is lower than the minimum allowable logic 1 at an inverter, the logic 1 output may not be correctly interpreted by the inverter. Likewise, a logic 0 from the gate array above the maximum allowable logic 0 at the inverter could result in an improper or indeterminate result.
Traditionally, attempts to address SSN have involved physically spreading drivers/pins, differential signaling, skewing the timing between groups of drivers, and/or adding resistors to the circuitry. However, these may be detrimental to performance, cost, design margin, and/or complexity from a packaging perspective.